Variabilidade especial e sazonalidade da circulação barotrópica da plataforma continental do Ceará

Abstract

The study of tides and winds, major forcing of the circulation within the continental shelf, has been improved in the last few years due to hydrodynamic modelling techniques. The objective of this study is to understand the spatial and seasonal barotropic circulation on the continental shelf of Ceará (PCCE). For the first time, the connectivity and dispersion processes of materials from the seven major estuaries in the region (Acaraú, Curú, Ceará, Cocó, Pacoti, Pirangi and Jaguaribe) is performed using passive floats. This study was done by using the ROMS model. A high-resolution grid between 35.7 ° and 42 ° W and 1 ° and 5 ° S is used in our studies. Three experiments were performed: PCCE-1, forced by tidal data from the global model TPXO 7.2; PCCE-2, forced by monthly climatology of winds data from the satellite QuikScat; and PCCE-3, with both forcings. For each experiment the model was ran for one year and the interconnection of estuaries is studied releasing floats in the entrance of each estuary. The model was validated using sea level data collected at IBGE and IHO stations (Porto do Mucuripe, Acaraú, Camocim and Timonha). The elevation values ranged from -1,7 to 1,6 m in the spring tide and between -0,8 and 0,7 m in neap tide. The largest values were found on the continental shelf and the western area. Tidal currents varied between 0,005 and 0,78 m/s and showed flow normal to the coast, presenting cyclic movements during the ebb-flood cycles. Higher intensities are in the west and near the shelf break. The residual tidal currents varied between 0,0005 and 0,006 m/s and showed no predominant direction, being higher in the west and near the shelf break. The elevation due to wind varied between 0,0001 and 0,0015 m, being higher in the winter due to increased wind speed. The wind driven currents varied between 0,002 and 0,04 m/s and are also higher during winter time. There was no significant difference between the elevations and the currents in the experiments PCCE-2 and PCCE-3, since the residual elevation and residual tidal currents are very small. The currents generated by wind and by wind and residual tide showed predominant northwesterly direction. The tide alone is not important in the transport of the floats in the PCCE when compared with the results for wind and wind and tides showing that the wind driven currents are the main forcing to the connectivity between the estuaries. The connectivity is mainly in east-west direction. Although more intense, tidal currents are cyclic, which makes the interaction between wind and residual tidal currents the main transport agent in PCCE.